What is the difference between instantaneous rate of a reaction and rate constant?

Explanation

Difference between Rate of a reaction and Rate constant
S.No. Rate of a reaction
1. Except for a zero order reaction, it changes with the progress of reaction.
2. For a reaction it depends upon a number of factors like temperature, catalyst, pressure, surface area etc.
3. It is measured in mol `L^(-1)s^(-1)` or atm `s^(-1)`.
4. It is the change in molar concentration of reactants or products per unit time.
Rate constant
1. It does not change with the progress of the reaction.
2. For a reaction it depends only upon temperature.
3. Its units changes with order of reaction.
4. It is equal to the rate of the reaction when molar concentration of all the reactants is-unity.